1. Field of the Invention
The invention relates to a method for achieving higher availability of computer PCI adapters, and specifically for achieving higher availability by dynamically switching PCI adapters between host-controlled operation and IOP-controlled operation.
2. Background Information
A PCI (Peripheral Component Interconnect) adapter allows a computer to interface using a standard protocol with a variety of peripheral devices to input and output data to the computer. In current computer architectures, PCI adapters operate in only one of two modes, called “native” and “non-native.” A PCI adapter that operates under the control of the system processor is termed host-controlled, or “native”. A PCI adapter that operates under the control of a separate IOP (Input-Output Processor) is termed IOP-controlled, or “non-native.” For example, in the case of a non-native PCI adaptor, it becomes necessary to turn off all of the processes that are running on that PCI adapter, if it is desired to service the IOP. This may be for a short time if the replacement IOP is available and the concurrent maintenance action is performed right away. In other cases, the system could be down for a significant period of time awaiting replacement of the IOP.
Another problem inherent in current PCI adapters, which are able to operate only in either the “native” or “non-native” mode, is the lack of any capability for balancing the work load between the system processor and an IOP. If, for example, the PCI adaptor is running natively, i.e., under the system processor, and an I/O intensive job causes the overall system performance to decline, there is no current capability for switching the PCI adapters to run non-natively so as to off-load some of the work from the system processor to an IOP. Similarly, there is also no way in present systems to dynamically move non-native PCI adapters from an IOP that is experiencing high utilization so that they can run natively.